AI players get "help" to make up for their shortcomings, and by help I mean resource injections and by shortcomings I mean an acute lack of tactical skill.

Also it is entirely possible they stockpiled a butt tonne of RUs before you shut down their eco.

EDIT: OH YEAH, I ALMOST FORGOT ABOUT FUSION! DUUUHHH!!!!!!!!
Basically Fusion modules (build them on your scavengers/service depots etc) allow you to generate RUs without doing any mining. The income is tiny at first but if you invest enough into upgrading it, it does give you some pretty nice returns over time.

Tbh I don't see why we don't have an option to turn that off, we can only dictate how much help they get (easy, normal, hard etc) and how they behave (defensive, aggressive etc) but then again AI difficulty is a vanilla feature IIRC so it may not be possible to code an option to turn it off completely, AI help being hardcoded in.

The real kicker is, the AI in complex is honestly much better than the vanilla AI. It's an actual challenge for me to fight one AI in this mod, and yet I once played a Free For All against 3 CPU players in vanilla (hard ones) and wiped the floor with them.

The game is designed to give the CPU free units. It does not matter if the CPU has harvester or not it will build in Tiers and Waves. This the original programming. The CPU does not have to research or worry about resources it just builds everything at top tier for free. Want to get really frustrated try easy Raiders, it will overwhelm you after 4 attacks with their ion ships.

Originally posted by Smooth-Kahuna:

The game is designed to give the CPU free units. It does not matter if the CPU has harvester or not it will build in Tiers and Waves. This the original programming. The CPU does not have to research or worry about resources it just builds everything at top tier for free. Want to get really frustrated try easy Raiders, it will overwhelm you after 4 attacks with their ion ships.

There is more than just the battlefield mode you know